The present invention relates to a downhole plug, especially for use in oil and gas wells, which contain high pressure and temperature.
For the sealing of oil and gas wells which are to be either temporarily or permanently shut off, generally, a downhole plug is used which seals the well by means of expanding gaskets. In wells under high pressure (e.g. higher than say 5000 psi), combined with high temperature (e.g. higher than 150° C.), gaskets containing elements of rubber or some other elastomer will have a limited operating life. Thus, downhole plugs having metal gaskets which can stand exposure to substantially higher pressures and temperatures than pure elastomer gaskets have been proposed.
EP patent specification 1277915 (Shell Int. Research, 2003) discloses the making of downhole plugs where the gasket element comprises a series of metal sleeves, positioned after each other along a core, and having an edge overlap. To seal, the metal sleeves are pressed together in such a way that they are forced to slide upon each other, forming a thicker stack. This design, however, is structurally weak when removing the downhole plug after use.
WO03058026 (Flaaten et. al., 2003) discloses a downhole plug, having a sealing sleeve with a meander-shaped ring element, which is in a cylindrical plane, and which expands radially, by axial compression against the tops of the meander-shape. In this way, sealing is achieved along the support surface of the element against the wall of the well. A substantial disadvantage with this sealing sleeve is that it does not contract when the axial pressure effect is removed. This proposal is thus not very suitable for downhole plugs, intended to temporarily seal wells, and to be removed after use.